Mid-top for three way

[Dr.EM]

Hello, I am planning (and only planning at this stage) a 3 way system. I'm thinking about the mid-top speaker section as it would be one of the first things I could do if I build this.

I have chosen the Vifa XG18 and Morel MDT33 drivers for it. They will be electronically crossed with 24db LR filters (practically essential with the sensitivity mismatch) at between 2.2-3.5k (to be defined through listening tests primarily). I am currently planning to use a sealed enclosure; WinISD is showing 15.8 litres as the optimal size, response starts to roll off slowly at about 200hz. The low crossover will be between 200-270hz.

I am planning a laminated style enclosure in plywood. I am thinking about trying the B&W type shape attached. It seems it should help minimise baffle diffraction as well as reducing internal standing waves. With the laminated style construction I will also add the random wavy cuts on the inside to again reduce resonances. A single cross shaped brace will likely be integrated also.

I want to stuff the enclosure quite significantly to reduce any reflected waves exiting through the mid cone, how will this effect the dimensions I should use? Will it need to be made larger or is it not significant?

I believe there are programs to model baffle diffractions, does anybody know of them; are they free

The distance between the mid and tweeter can be quite critical I hear, how do you decide this distance. Are there equations/programs to help?

How difficult is the laminated style construction? I gather there will be a template to follow with a router? I haven't used a router before so will probably need some practise. Layers can be aligned by clamping then dowelling in stages, making gluing easier i'm thinking.

If constructed well could this design exhibit much better quality than B&W DM602s I have now? I find they have harshness and not a very open mid. Input appreciated

[owdi]

TheEdge is a quick baffle diffraction sim, very easy to use
BDS has more features***, but is more difficult to use.

I find myself using TheEdge much more than BDS, because it's much easier to quickly check off axis response. Despite spending hours in both programs, I still managed to screw up my last baffle :-)

*** TheEdge can do a few things that BDS cannot, like model open baffles, and baffle with more than 4 corners.

The distance between the woofer and tweeter is critical. The closer they are, the better your vertical dispersion will be. With my current project, I'm having lot's of trouble pulling the listening axis down to tweeter level with only 14.5cm between the center of the tweeter and woofer.

Dan

[Dr.EM]

Thanks a lot, I'll have a play with those

Did I see you've used an XG18 in one of your speakers? How do you find it, is it smooth sounding would you say?

I looked at some convertors earlier and am obviously missing something. Distance from centre to centre should be about 0.1 wavelength max of the frequency concerned (crossover frequency?). Calculators are showing the wavelength as 9993081.9333CM for 3Khz . Would be no problem if that was all there was to it

[Wingfeather]

Hi Dr. EM

My 3-way speakers were made using this method. What I did was design the templates (I made three different-shaped ones for different parts of the speaker) in Rhino3d, and had them professionally made. It cost about £65 IIRC.
I then duplicated the templates in 25mm MDF using a router with a template bit. It's a very easy process, but be warned - it takes a LOT of time. I think it was about a man-month to machine all the laminates for my speakers.

I ended up being somewhat unhappy with the deadness of my enclosures, despite the fact they are 2 inches thick at the front and back panels, and at least 1 inch thick everywhere else. Plus there's a lot of internal bracing. PLUS, I covered the inside with self-adhesive bitumen sheeting.
If I were to do it again I would want to try plywood or some other material.

AFAIK, it's nearly always best to simply make the distance between the mid and the tweeter as small as possible - it minimizes the comb filtering you get in the crossover region and makes the two units as close to a point-source as possible.

[Dr.EM]

Thanks for your input Wingfeather. Time is something I should have a lot of, since right now I have nowhere to put these speakers . Lots of time to make and test things out. I don't know if you made the bass enclosure laminated style too though, i'm only doing a mid-top which will likely be much smaller.

I'm suprised your cabinets didn't end up very dead sounding, they sound solid enough. I will make sure I use ply this time though, my first thought was mainly to stop too much nasty dust being produced.

Where did you get your templates done incidently?

[Dr.EM]

Some more thoughts on midranges. The XG18 looks good but I must consider these others.

Monacor SPH-165KEP, I like the look of the response of this driver, with it falling at higher frequencies and no emphasis around 5-6k. Probably difficult to mount and would likely look out of place aesthestically though.

Peerless 832873, good extension and overall quite flat. Flattened edges on basket could blend in well with rounded cabinet sides. Does rise in the top end though, not heard any subjective opinions.

Audax HM100Z0, really nice response and excellent subjective opinions. Very different utilisation to other (larger) mids though, needs to be crossed higher; may be a problem with a TL bass due to the rippled higher end response they produce (?). Also virtually impossible to obtain, if anyone knows of how to get them let me know . May be nice crossed to a ribbon tweeter.

[Dr.EM]

Ok, I thought about starting a new thread since this has changed quite a lot since my initial idea. Anyhow, I now have drivers and have been running tests for some time. I managed to get Audax HM100Z0 drivers and am using the Hi-Vi RT2E-A planar tweeter with them.

I am getting a very good overall sound even in the crude test setup. A 12db LR crossover is being used and the two channels of my amp are bi-amping the setup (meaning mono sound until I redo my burnt out chipamp ). There are problems with the sound though which I think (hope) are purely down to the very poor cabinet the mid is in. It is a cabinet from an old mini hi-fi, about the right volume but thin walls, no bracing, a ported design etc. It has little going for it really, I have completely stuffed it but am still getting lots of resonances. Are these likely to be purely cabinet based? The propsed cabinet is the polar opposite, thick walls, laminate construction, internal diffusion patterns, rounded baffle. But how likely is this to completely clear up the sound?

Also the speaker is running down low, it will be crossed 24db at about 420Hz, this should also help dramatically? Obviously a lot of midbass is missing as it is, making electric guitars etc sound thin, but it should also help the upper response by not letting it run down to its resonance?

[Dr.EM]

Ok, I think I will do an open back mid enclosure after some reading. I still plan a laminated enclosure and it will have the random internal cuts. Any ideas about how large an "enclosure" of this type needs to be? If the walls are quite close together how far back might it need to reach or is it fairly unimportant? I am not decided on baffle layout but probably won't be able to do the nice fully rounded enclosure. I plan just a rounding at the front. I have drawn some baffle layouts, the darker brown is where the rounding would be. Any ideas, the edge models them similarly. The side by side arrangement means I can make the bass units taller reducing the depth needed to make up thier volume, but it looks the worst imo

[Dr.EM]

perhaps as a final bid to make it as ugly as possible, or mabye a refinement, how about something like this (assuming I can get more mids) . The tweeter would be set into a waveguide cut in the wood itself("easy" with the laminate design), in order to achieve better time alignment. Are there specific dimensions for a waveguide that must be adhered to, Hi-Vi do a version of this tweeter with one and it just looks like an angled cut either side. Twin mids make for higher sensitivity (rather decent at 96db), but could they cause problems of lobing etc in the range of 400-4500hz? Is the spacing to the tweeter now too much? Will this design impact imaging quality? I want to get building these enclosures, but being so critical to the overall sound I want to do it right too!

[pinkmouse]

Looks easy enough to just knock up a test box out of chipboard or similar and test.